Memory devices are typically provided as internal, semiconductor, integrated circuits in computers or other electronic devices. There are many different types of memory including random-access memory (RAM), read only memory (ROM), synchronous dynamic random access memory (SDRAM), dynamic random access memory (DRAM), and flash memory.
Flash memory devices have developed into a popular source of non-volatile memory for a wide range of electronic applications. Flash memory devices typically use a one-transistor memory cell that allows for high memory densities, high reliability, and low power consumption. Common uses for flash memory include personal computers, personal digital assistants (PDAs), digital cameras, and cellular telephones. Program code and system data such as a basic input/output system (BIOS) are typically stored in flash memory devices for use in personal computer systems.
Conventional non-volatile memory cells employ floating gate device technology. A floating gate cell can be programmed by injecting electrons to the silicon floating gate by channel hot carrier injection (CHE) to put the cell into a high threshold state. The cell can be erased by hot hole injection from the substrate plus electron back-tunneling to the substrate by Fowler-Nordheim tunneling to put the cell in a low threshold state. Both mechanisms require high fields across the gate dielectric layers with resulting adverse effects in device characteristics and reliability.
CHE can consume large amounts of power for writing, generates interface states, degrades device transconductance, and enhances back-tunneling that affects charge retention and read-disturb. Fowler-Nordheim tunneling and associated hot-hole injection generates fixed charge centers in tunneling dielectrics and shallow traps and defects in the trapping layer, thus breaking stable bonds and eventually degrading the dielectric properties of the device.
As computers become smaller and their performance increases, the computer memories have also gone through a corresponding size reduction and performance increase. However, flash memory devices present a challenge in scalability due, at least in part, to the high programming voltages typically required. Their performance can also suffer due to the above-discussed limitations.
For the reasons stated above, and for other reasons stated below which will become apparent to those skilled in the art upon reading and understanding the present specification, there is a need in the art for a more scalable, higher performance non-volatile memory device.